1. Field of the Invention
The present invention relates to rotary cutters such as a face milling cutter, a side milling cutter or the like, and in particular to improvements for strengthening a cutting edge thereof while permitting the application of a large rake angle to reduce a cutting load exerted thereon.
2. Prior Art
FIGS. 8 to 13 depict a conventional face milling cutter 1, which comprises a cutter body 2 having an axis of rotation therethrough and having a plurality of chip pockets 5 formed in circumferentially distributed relation to one another so as to open to a forward axial face 3 and a circumferential surface 4. An insert receiving recess 6 is formed in the wall of each chip pocket facing in a direction of rotation of the body 2, and a generally square, indexable cutting insert 7 formed of cemented carbide is received in each insert receiving recess 6 with a seat member 8 and a supporter 9 interposed therebetween, and is releasably secured thereto by means of an insert securing wedge 10 and a supporter securing wedge 11.
The face milling cutter 1 is provided with a main cutting edge 12 directed radially outwardly and an auxiliary cutting edge 13 directed axially forwardly of the tool body 2, and cuts a workpiece by these cutting edges.
In the face milling cutter 1 as described above, the axial rake angle for the cutting edge is determined appropriately by taking the cutting conditions into consideration. When the axial rake angle is set so as to be positive and large, cutting chips of helical shapes are produced, and the cutting load is reduced. Such a tool is paticularly effective for the prevention of chattering, and can be suitably used for cutting a workpiece of less rigidity or for a cutting operation with a machine of less power. However, when the axial rake angle is made large, the included angle is increased since an appropriate relief angle (5.degree. to 6.degree. ) must be ensured. Accordingly, the strength of the cutting edge deteriorates, and the resulting tool is susceptible to fracturing when cutting a surface as forged or a hard workpiece.
In order to circumvent the above problems, the face milling cutter has been conventionally modified as shown in FIGS. 10 to 12, in which the main and auxiliary cutting edges 12 and 13 are honed to provide honed portions 14 of a prescribed width S, which are inclined with respect to the rake surface at a prescribed inclination angle .theta., whereby the strength of the cutting edges are enhanced. In this modification, however, when the axial rake angle A.sub.1 is increased to above 30.degree. as indicated by a two-dot chain line in FIG. 13, the included angle .beta. for the auxiliary cutting edge 13 becomes less than 55.degree.. Therefore, the above modification of the tool is not successful in obtaining a sufficient strength at the cutting edge, and the cutting edges of the resulting tool are still susceptible to fracturing.